Access Image Files from a DSLR

Like the titel says, i want to access the image files of my DSLR connected to the computer via USB. In detail I want to copy the files to a directory on my HDD for further processing.
I searched the web but couldn't find any hint about how to access a dslr files (of any brand). Since I can access them via the File Browser of my PC i guess ther must be a way to get there but i have really no clue since the memory card where the pictures are stored isn't pluged in as a storage device with a device name (C:, D:, etc).
Would be very thankfull for any push into the right direction

Ok i ate the nikon SDK and found out you can access the camera via PTP (Picture Transfer Protocol). But still i have no idea how to. The Microsoft msdn site doesn't realy gives a hint how to, just that u can do it. Any one with experience about this here?